This invention relates to a method for the manufacture of highly loadable components by precision forging, preferably compressor or turbine blades or similar components with different stress and volume zones.
Turbine or compressor blades for aircraft engines are, as is generally known, manufactured by hot forging a blank made of usually cylindrical starting material to a near-net-shape preform in a multitude of subsequent forming operations, if applicable with intermediate deburring and surface treatment, as well as heat treatment to re-crystallization. From the preform, which in this case already comprises an airfoil, a platform and a blade root, the final form of the blade is then produced in further processing operations, for example deburring, cleaning, cold forging or surface treatment.
In Specification GB 727 688, a method for the manufacture of precision components with complex contours is described on an example of turbine blades in which a preform is initially forged from bar-type starting material in several hot-forming operations and subsequently, after deburring and cleaning, a blade with precise shape and size is subsequently produced in one cold forming operation under high pressure. In the method described in Specification U.S. Pat. No. 6,138,491, a preform is likewise initially forged from a cylindrical blank and subsequently finally shaped in a forging die. According to Specification U.S. Pat. No. 5,173,134, titanium-alloy compressor disks and blades for aircraft engines are made in that a preform is first produced by hot forging which is subsequently finish-forged by hot forming in a die.
The individual elements of the blade, viz. airfoil, platform and root, have, on the one hand, zones of considerably different volume and, on the other hand, are subject to different loads in the individual blade areas (partially) during operation in the aircraft engine. While the upper part of the airfoil has a particularly small volume and the center part of the blade, comprising the platform and the lower airfoil part as well as the upper root part, has a large volume, the remaining bottom part of the root has an approximately medium volume, as compared to the above-mentioned volume zones. This reflects the different degrees of forming required in the respective volume zones of a uniformly shaped, for example cylindrical, blank.
Also different in the individual volume zones is the load occurring during operation. While a dynamic load in the high-frequency range occurs in the upper airfoil part with its small volume and a high static load in the center blade part with its large volume, the load in the bottom part of the blade with its medium volume is rather low.
Depending on the forming forces and the volumes deformed, the forming process as well as the heat treatment and recrystallization operations performed subsequently to the forming operations furthermore result in a microstructure which satisfies the required strength properties. The number of forming operations for the final product with different volume zones forged from an evenly shaped, for example cylindrical, starting stock is actually controlled by the shape to be achieved, not by the structural formation required to obtain the necessary strength. This means, however, that the workpiece is further processed with considerable forming and intermediate processing effort to the final component geometry even if the strength properties desired and the corresponding structure required are achieved with only a few forming operations. Conversely, it is very likely that the required microstructure is not achieved in certain volume zones with only small volume change and correspondingly low forming action.